1. Field of the Invention
The present invention relates to a method of and an apparatus for preparing an oxide superconducting film using laser ablation.
2. Description of the Background Art
Formation of an oxide superconducting film by excimer laser ablation, for example, is watched with interest in the point that it is possible to implement a high-quality film. In general, a pulse laser beam is employed for such laser ablation.
In an already reported method of preparing an oxide superconducting film using laser ablation, a high-quality oxide superconducting film is obtained when the laser beam is set at a repetition rate of not more than about 10 Hz so that the film forming rate is less than about 2000 .ANG./min.
When an oxide superconducting film is formed by ordinary laser ablation, the laser repetition rate is so increased as to increase the film forming rate. However, if the film forming rate is increased in excess of 2000 .ANG./min., for example, the as-formed oxide superconducting film is obtained as an aggregate of fine crystal grains of not more than 1 .mu.m in size, and its critical temperature and critical current density are reduced in response to clear appearance of grain boundaries.
In a method of preparing an oxide superconducting film using ordinary laser ablation, it is necessary to heat a substrate to a temperature of at least 600.degree. C., in order to facilitate crystallization of the oxide superconducting film, which is deposited on the substrate. Therefore, available materials for such a substrate are restricted to ceramic materials, single-crystalline materials of MgO, SrTiO.sub.3 and the like, which are still unreactive with film components at such a high temperature, and it is impossible to use a substrate of a metal, for example.